The present invention relates to a liquid crystal device and, in particular, to a structure of a liquid crystal device capable of switching between reflection type display and transmission type display and to an electronic apparatus using this liquid crystal device.
Conventionally, a reflection type liquid crystal device, which consumes little power, has been widely used as a display section attached to a portable device or apparatus. It has a problem in that it makes the display visible by utilizing external light, so that it is impossible to read the display in a dark place. In view of this, a liquid crystal device has been proposed which, in a light place, utilizes external light as a usual reflective type liquid crystal device but which, in a dark place, enables the display to be seen by means of an inner light source. As disclosed in Japanese Utility Model Laid-Open No. 57-049271, in this proposed device, a polarizing plate, a transflective plate, and a backlight are arranged in this order on the outer surface of the liquid crystal panel, which is the side opposite to the observation side. In this liquid crystal device, when it is light surroundings, external light is taken in and the light reflected by the transflective plate is utilized to effect reflection type display. When it becomes dark, the backlight illuminates and the display is made visible by the light transmitted through the transflective plate, thus effecting transmission type display.
Japanese Patent Laid-Open No. 8-292413 discloses another liquid crystal device in which the brightness of the reflection type display is improved. In this liquid crystal device, a transflective plate, a polarizing plate, and a backlight are arranged in this order on the outer surface of the liquid crystal panel on the side opposite to the observation side. Under the light surroundings, external light is taken in and the light reflected by the transflective plate is utilized to effect reflection type display, and under the dark surroundings, the back light illuminates and the display is made visible by the light transmitted through the polarizing plate and the transflective plate, thus effecting transmission type display. In this construction, there is no polarizing plate between the liquid crystal cell and the transflective plate, so that it is possible to achieve a reflection type display brighter than that of the above-described liquid crystal device.
However, in the liquid crystal device disclosed in Japanese Patent Laid-Open No. 8-292413, a transparent substrate exists between the liquid crystal layer and the transflective plate, resulting in a double image, a smeared image, etc.
Further, nowadays, as portable apparatus, OA apparatus, etc. are developed, a colored display is required of liquid crystal devices, and in many apparatuses using reflection type liquid crystal devices, a colored display is required. However, in the system as disclosed in the above-mentioned publication, in which a liquid crystal device is combined with a color filter, the transflective plate is arranged behind the liquid crystal panel, so that a thick transparent liquid crystal panel exists between the liquid crystal layer or the color filter and the transflective plate, with the result that a double image, a smeared image, etc. are generated by parallax, making it impossible to achieve a satisfactory color development.
To solve the above problem, Japanese Patent Laid-Open No. 7-318929 proposes a transflective type color liquid crystal device in which a reflecting plate is arranged so as to be in contact with the liquid crystal layer. However, in this liquid crystal device, it is impossible to recognize the display in the dark surroundings.
On the other hand, a transflective type liquid crystal device has been proposed in Japanese Patent Laid-Open No. 7-318929 in which a pixel electrode also serving as the transflective layer is formed on the inner surface of the liquid crystal cell. Further, disclosed is a construction in which a pixel electrode consisting of an ITO (indium tin oxide) layer is superimposed on a transflective layer consisting of a metal layer through the intermediation of an insulating layer. Further, in this liquid crystal device, on the back side of the liquid crystal cell, there is no optical element which varies the polarization of the incident light from the backlight between the transflective plate and the polarizing plate, so that the incident light from the backlight always impinges upon the liquid crystal cell as linearly polarized light passing through the polarizing plate. As a result, when the optical characteristics of the polarizing plate and the phase plate on the front side of the liquid crystal cell, and the liquid crystal cell, etc. are set so as to enhance the contrast characteristic at the time of reflection type display, it is impossible to achieve a satisfactory contrast characteristic at the time of transmission type display. Conversely, when the optical characateristics of these components are set so as to enhance the contrast characteristic at the time of transmission type display, it is impossible to achieve a satisfactory contrast characteristic at the time of reflection type display. Similarly, when the optical characteristic of these components are set so that the color compensation for the color due to wavelength dispersion of light may be effected in a satisfactory manner at the time of reflection type display, such color compensation cannot be effected in a satisfactory manner at the time of transmission type display. Conversely, when the optical characteristics of these components are set so that such color compensation may be effected in a satisfactory manner at the time of reflection type display, such color compensation cannot be effected in a satisfactory manner at the time of transmission type display. That is, generally speaking, it is very difficult to achieve high contrast or effect color compensation in a satisfactory manner at the time of both reflection type display and transmission type display, making it impossible to effect high quality image display.
The present invention has been made in view of the above problem. It is accordingly an object of the present invention to provide a transflective type liquid crystal device of type which is capable of switching between reflection type display and transmission type display, wherein a double image or smeared image due to parallax is not generated, making it possible to effect high quality image display at the time of both reflection type display and transmission type display and an electronic apparatus using such a liquid crystal device.
To achieve the above object, there is provided, in accordance with the present invention, a liquid crystal device comprising a pair of first and second transparent substrates, a liquid crystal layer held between the first and second substrates, a laminate which is formed on the liquid crystal layer side surface of the second substrate and in which at least a transflective layer and a transparent electrode layer are stacked together, an illuminating device arranged on the side of the second substrate which is opposite to the liquid crystal layer, a first polarizing plate arranged on the side of the first susbstrate which is opposite to the liquid crystal layer, a first phase plate arranged between the first substrate and the first polarizing plate, a second polarizing plate arranged between the second substrate and the illuminating device, and a second phase plate arranged between the second substrate and the second polarizing plate.
In the liquid crystal device of the present invention, at the time of reflection type display, the laminate reflects external light coming from the first substrate side to the liquid crystal layer side by the transflective layer included therein. Since the laminate is arranged on the liquid crystal layer side of the second substrate, there is scarcely any gap between the laminate and the liquid crystal layer, so that a double image display or a smeared image due to parallax is not generated. On the other hand, at the time of transmission display, the laminate allows the light source light emitted from the illuminating device and coming from the second substrate side to be transmitted to the liquid crystal layer side through the transflective layer and the transparent electrode layer included therein. Thus, in a dark place, a bright display is possible by using the light source light. This transflective layer may consist of a reflection layer provided with minute openings or designed such that light can be transmitted through a region thereof, or a layer exhibiting semi-transmission-reflection property over the entire area (for example, a thin metal layer thin enough to allow light to be transmitted therethrough or a half mirror on the market).
In the liquid crystal device of the present invention, in particular, external light reflected by the non-opening area (reflection area or non-transmission area), where no opening, gap, etc. is formed, of the transflective layer is transmitted through the transparent electrode layer stacked on the transflective layer and transmitted through the liquid crystal portion driven by the transparent electrode layer portion opposed to the non-opening area. That is, reflection type display can be effected by using the liquid crystal portion through longitudinal electric field by the transparent electrode layer portion opposed to the non-opening area. On the other hand, the light transmitted through the opening area (non-reflection area or transmission area) of the transflective layer, where an opening, gap, etc. is formed, is transmitted through the transparent electrode layer stacked on the transflective layer and transmitted through the liquid crystal portion driven by the transparent electrode layer portion opposed to the opening area. That is, transmission type display can be effected by using the liquid crystal portion driven through longitudinal electric field by the transparent electrode layer portion opposed to the opening area. In this way, no matter what the pattern of the transflective layer may be, the electric field applied to the liquid crystal layer by the transparent electrode layer is not affected, so that, independently of the opening pattern or the gap pattern of the transflective layer, the alignment of the liquid crystal is uniform in each dot or each pixel at the time of reflection type display and at the time of transmission type display, whereby it is possible to prevent a deterioration in display quality due to disturbance of the alignment.
Further, in the liquid crystal device of the present invention, there are provided a first polarizing plate and a first phase plate and a second polarizing plate and a second phase plate, so that display control can be effected in a satisfactory manner in both reflection type display and transmission type display. More specifically, the influence of color, etc. due to light wavelength dispersion at the time of reflection type display on the color tone can be reduced by the first phase plate, and the influence of color, etc. due to light wavelength dispersion at the time of transmission type display on the color tone can be reduced by the second phase plate. Regarding the first and second phase plates, it is also possible to respectively arrange a plurality of phase plates, depending on color compensation or visual angle compensation. When a plurality of phase plates are used as the first or second phase plates, optimization of color compensation or visual angle compensation can be more easily effected. Further, the optical characteristics of the first polarizing plate, the first phase plate, the liquid crystal layer, and the transflective layer are set such that the contrast in reflection type display is enhanced, and, under this condition, the optical characteristics of the second polarizing plate and the second phase plate are set such that the contrast in transmission type display is enhanced, whereby it is possible to obtain high contrast characteristic in both reflection type display and transmission type display.
As the material of this transflective layer, a metal whose main constituent is Al (aluminum) is used. However, the material is not particularly limited as long as it is a metal capable of reflecting external light of visible range, such as Cr (chromium) or Ag (silver).
As the drive system for the liquid crystal device of the present invention, it is possible to adopt various well-known drive systems, such as passive matrix drive system, TFT (thin film transistor) active matrix drive system, TFD (thin film diode) active matrix drive system, and segment drive system. In many cases, the voltage-reflectance (transmittance) characteristic of the liquid crystal cell differs between reflection type display and transmission type display, so that it is desirable to make the drive voltage different between reflection type display and transmission type display, optimizing it for each. Further, on the first substrate, a plurality of stripe-like or segment-like transparent electrodes are formed according to the drive system, or a transparent electrode is formed over the entire first substrate. Alternatively, it is also possible to drive through a lateral electric field parallel to the substrate between the transparent electrodes on the second substrate, without providing an opposite electrode on the first substrate.
In a form of the liquid crystal device of the present invention, the transflective layer, a color filter, a protective layer and the transparent electrode layer are stacked in the laminate in that order from the side nearest to the second substrate.
In this form, a color filter is further provided on the transflective layer, so that it is possible to effect reflection type color display by external light and transmission type color display utilizing an illuminating device. It is desirable that the color filter exhibit a transmittance of not less than 25% to all the light in wavelength range of not less than 380 nm and not more than 780 nm. This makes it possible to realize bright reflection type color display and transmission type color display.
Usually, a metal whose main constituent is Al is used for the transflective layer. However, an Al metal is little resistant to solvent and difficult to handle. Further, it is subject to flaws. However, in this form, the reflecting surface of the transflective layer formed of an Al metal or the like is covered with a color filter and a protective layer to form a transparent electrode layer, so that Al is not brought into direct contact with the developer for forming a transparent electrode such as ITO layer. Thus, the Al metal is easier to handle, and less subject to flaws, etc. For this protective layer, it is possible to use a material such as an acrylic transparent resin or silicon oxide.
The protective layer between the color filter and the transparent electrode layer may be omitted. This applies to the case in which the present invention is used as an opposite substrate to a substrate with an active element of a TFT active matrix type liquid crystal device and in which patterning is not needed for the transparent electrode layer of the opposite substrate.
In another form of the liquid crystal device of the present invention, in the laminate, there are stacked the transflective layer, an insulating layer and the transparent electrode layer, in that order from the side nearest to the second substrate.
In this form, it is possible to insulate the transparent electrode layer and the transflective layer by the insulaing layer, so that even if the transflective layer is formed in an arbitrary pattern of a conductive metal such as Al, no problem is generated in the insulating condition of the transparent electrode layer due to the presence of the transflective layer. Further, the reflecting surface of the transflective layer formed of an Al metal or the like is covered with an insulating layer to form a transparent electrode layer, so that the Al is not brought into direct contact with the developer for forming the transparent electrode such as an ITO layer. Thus, the Al metal is easier to handle and less subject to flaws or the like.
In the form in which the insulating layer is also stacked in this laminate, a color filter and a protective layer may be formed on the liquid crystal layer side surface of the first substrate, in that order as from the side nearest to the first substrate.
In this construction, by utilizing the color filter which is formed not on the second substrate side but on the first substrate side and which is protected by the protective layer, it is possible to effect reflection type color display by external light and transmission type color display utilizing an illuminating device.
In the form in which the insulating layer is also stacked in the laminate, the insulating layer may be formed by oxidizing the surface portion of the transflective layer.
In this form, it is possible to obtain a very thin insulating layer having high insulation property. In this case, it is desirable to use aluminum as the transflective layer. This is because aluminum can maintain its reflectance if oxidized. When thus oxidizing the insulating layer, the transflective layer may undergo anodic oxidation or thermal oxidation.
In the form in which the insulating layer is also stacked in the laminate, the insulating layer may be formed by stacking together two or more different insulating layers.
In this construction, it is possible to enhance the insulating property of the insulating layer. As one of the insulating layers, it is possible to use an oxide of aluminum or the like, and, as the other insulating layer, it is possible to use an SiO2 (silicon oxide) layer, an overcoating layer using an organic substance. When forming an SiO2 layer, evaporation, sputtering, CVD method or the like is used. When forming an organic film, spin coating or the like is used.
In the form in which an insulating layer is also stacked in the laminate, it is also possible for a color filter to be further stacked in the laminate between the insulating layer and the transparent electrode layer.
In this construction, it is possible to form on the first substrate a laminate in which a transflective layer, an insulating layer, a color filter and a transparent electrode layer are stacked together, and it is possible to protect the transflective layer with the insulating layer and to effect a reflection type color display using external light and a transmission type color display utilizing an illuminating device. In particular, since the reflecting surface of the transflective layer of Al metal or the like is covered with an insulating layer, and a color filter and a transparent electrode layer are formed, the Al is not brought into direct contact with the developer for forming the color filter or the developer for forming the transparent electrode.
In this case, further, a protective layer may be formed in the laminate between the color filter and the transparent electrode layer.
In this construction, it is possible to form on the first substrate a laminate in which a transflective layer, an insulating layer, a color filter, a protective layer and a transparent electrode layer are stacked together, and it is possible to protect the transflective layer with the insulating layer and to protect the color filter with the protective layer and, further, to perform a reflection type color display using external light and a transmission type color display utilizing an illuminating device.
In the form in which an insulating layer is also stacked in the laminate, it is possible to further provide an active element formed on the insulating layer and connected to the transparent electrode layer.
In this construction, it is possible to form an active drive type liquid crystal device capable of high quality reflection type and transmission type display by using an active element insulated from the transflective layer by the insulating layer. Here, as the active element, it is possible to use a three terminal element such as TFT element or a two terminal element such as TFD element.
In another form of the liquid crystal device of the present invention, a plurality of openings are formed in the transflective layer.
In this form, when there is enough external light, it is possible to perform reflection type display by taking in external light and reflecting it by the non-opening portion of the transflective layer. When there is not enough external light, the illuminating device is lighted, and the light source light is introduced into the liquid crystal layer through the opening of the transflective layer, thereby making it possible to perform transmission type display. It is desirable for the diameter of the opening to be not less than 0.01 xcexcm and not more than 20 xcexcm. Due to this arrangement, it is difficult for the human eye to recognize, and it is possible to restrain the deterioration in the display generated due to the provision of the opening, making it possible to realize both reflection type display and transmission type display. Further, it is desirable that the opening be formed in an area proportion of not less than 5% and not more than 30% with respect to the transflective layer. This makes it possible to restrain the decrease in the brightness of the reflection type display and, further, to realize transmission type display by the light source light introduced into the liquid crystal layer through the opening of the transflective layer.
In another form of the liquid crystal device of the present invention, a plurality of the transflective layers are formed at predetermined intervals.
In this form, transmission type display can be realized by the light source light emitted from the illuminating device and introduced into the liquid crystal layer through the gaps of the plurality of transflective layers formed linearly. In this case also, it is desirable for the gap of the transflective layers to be not less than 0.01 xcexcm and not more than 20 xcexcm, and the gap of the transflective layers is preferably formed in an area proportion of not less than 5% and not more than 30% with respect to the transflective layers.
In another form of the liquid crystal device of the present invention, the device is in a dark (black) state when it is not being driven.
In this form, since the device is in a dark state when it is not being driven, it is possible, in transmission type display, to restrain light leakage between pixels or dots where the liquid crystal is not driven, whereby it is possible to obtain a transmission type display of higher contrast. Further, in reflection type display, it is possible to restrain reflected light unnecessary for display from between pixels and dots, so that it is possible to obtain a display of higher contrast. In this way, it is possible in general to achieve an improvement in contrast in transmission type display and reflection type display without providing a light shielding layer called black matrix or black mask at a position opposed to the gap of the reflection electrode. In addition, by providing such a light shielding layer, it is also possible to prevent the brightness in reflection type display from being reduced.
In another form of the liquid crystal device of the present invention, the above-mentioned transflective layer contains 95% by weight or more of Al, and its thickness is not less than 10 nm and not more than 40 nm.
In this form, it is possible to obtain a satisfactory transmittance and reflectance by a relatively thin transflective layer. According to an experiment, it is possible to prepare a transflective layer in which the transmittance is not less than 1% and not more than 40% and the reflectance is not less than 50% and not more than 95% within this thickness range.
In another form of the liquid crystal device of the present invention, a scattering plate is further provided on the opposite side to the liquid crystal layer of the first substrate.
In this form, it is possible to show the mirror surface feel of the transflective layer on the scattering surface (white surface) by means of the scattering plate. Further, due to the scattering by the scattering plate, it is possible to realize a display of a wide angle of view. The scattering plate may be at any position as long as it is on the opposite side to the liquid crystal layer of the first substrate. Taking into account the influence of backscattering of the scattering plate (scattering to the incident light side when external light is incident), it is desirable to arrange it between the first polarizing plate and the first substrate. The backscattering is scattering light that has nothing to do with the display of the liquid crystal device; when there is this backscattering, the contrast in reflection type display is deteriorated. By arranging it between the first polarizing plate and the first substrate, it is possible to reduce approximately by half the light quantity of the backscattering by means of the first polarizing plate.
In another form of the liquid crystal device of the present invention, the transflective layer has recesses and protrusions.
In this form, it is possible to eliminate the mirror surface feel of the transflective layer by the protrusions and recesses and show it as a scattering surface (white surface). Further, due to the scattering by the recesses and protrusions, it is possible to realize a display of a wide angle of view. These recesses and protrusions can be formed by using a photosensitive acrylic resin or the like as the base of the transflective layer, or by roughening the base glass substrate itself by hydrofluoric acid. Further, it is desirable to further form a transparent flattening layer on the recess/protrusion surface of the transflective layer to flatten the surface facing the liquid crystal layer (the surface forming the alignment layer) from the viewpoint of preventing alignment defect of the liquid crystal.
The above object of the present invention can be achieved by an electronic apparatus equipped with the liquid crystal device of the present invention described above.
In accordance with the present invention, it is possible to realize various electronic apparatuses using a transflective type liquid crystal device or a transflective type color liquid crystal device free from a double image or smeared image due to parallax and capable of effecting display switching between reflection type display and transmission type display. Such an electronic apparatus can realize a high image quality display independently of the ambient external light in a light place or a dark place.